Numerous mechanisms have been proposed to explain how the flanks of stratovolcanoes collapse. However, the usefulness of different models has been difficult to quantify, partly because of large uncertainties in rock strength. Recent comprehensive measurements of the geotechnical properties of fresh and hydrothermally altered volcanic materials from Teide, Tenerife are used to improve our understanding of the destabilising potential of different volcanic and non-volcanic processes. A parameter sensitivity analysis has been undertaken, and this allows the first order effects of pore-fluid pressures, magmatic intrusions and transient stresses to be assessed, both individually and in conjunction with other processes. We have assessed the stability of the flanks of Teide through a combined 2D approach of finite element, and limit equilibrium methods. The analysis shows that a circular magmatic intrusion through a central conduit beneath the summit has no effect on the stability of the edifice, whereas a dyke can change the stress regime, increasing the potential for yielding at the break in slope at the base of the edifice. We also show how the depth of potential failure planes is related to cohesion. The effects of peak ground accelerations and pore pressures on stability are presented in ways that show their importance, both individually and when combined in failure planes at different depths. Our analysis of Teide, which takes into account our recent analysis of structural features and hydrothermal alteration on the volcano, suggests that Teide is currently stable (factor of safety 1.3–1.8), and will continue to be so in the event of magmatic intrusions and seismic shocks of magnitudes within the expected range. While the analysis is based on Teide, the analysis and results have potential application to many other stratovolcanoes.